There are many situations in which it is desirable to provide for temporal comparison of images. In the field of medicine, it can be critical for proper diagnosis to have the ability to view a portion of the surface of the human body over time. Historically, this has been done by the use of physician's notes regarding previous examination of the area in question, in comparison to the present-time observation of that area. However, such methods require an inordinate amount of the physician's time, and often at best provide only a rough comparison that may be insufficient for diagnosing certain conditions such as melanoma.
Physicians have also used photography to aid in this temporal comparison. The physician may compare photographs of the body portion taken at different times, or compare photographs directly to the portion of the body surface. However, these methods at best provide juxtaposition of images that requires the physician to use judgment in detecting sometimes subtle changes to the body surface. In one attempt to produce juxtaposed images which are at least oriented in a similar manner to simplify this comparison, there has been used a system that displays on a CRT a previously-taken image next to a live video image. The physician may then rotate the video camera until the live image is perceived to be in the same orientation as the stored image. This method, however, still requires the physician to estimate by eye subtle changes in the surface area that may be indicative of serious disease.
Another area where temporal comparison of images is important is in the testing of cutaneous pharmaceuticals and cosmetics. Before and after photographs of regions of skin are often used to document the benefits of a treatment. A method of aligning images, particularly with a means for controlling and standardizing lighting conditions, would provide more reliable before and after photographs where changes in the images could more reliably be related to the treatment rather than the image acquisition conditions including camera alignment and lighting changes.